1. Field of the Invention
This invention relates to a semiconductor device which has a high dielectric constant thin film as an insulating film used for a gate insulating film or the like and a metallic material as an electrode used for a gate electrode or the like and to a method of manufacturing the semiconductor device.
2. Description of the Related Art
As LSIs have recently been getting much denser and much faster, elements in LSIs have been miniaturized more. With the further miniaturization, there have been demands for silicon oxide (SiO2) films to be made still thinner in a capacitor and/or a transistor as component elements in a MOS structure. When the thickness of a SiO2 film becomes as thin as 3 nm or less, electrons start to flow through a direct tunneling under an electric field where the device operates, which causes the problem of increasing leakage current and therefore increasing the power consumption of the device and other problems.
To overcome the problems, a next-generation gate insulating film replaceable with the SiO2 film has been desired and a high dielectric constant film has been attracting attention. The reason is that a high dielectric constant film with the same capacitance as that of a SiO2 film is thicker than the latter. Making the insulating film thicker makes it possible to decrease the probability that electrons will tunnel through the insulating film or to suppress tunnel current to a low level.
As a high dielectric gate insulating film replaceable with SiO2, hafnium (Hf)-silicate has been nominated. In addition, to suppress the depletion in the gate electrode, it is desirable that the Hf-silicate should be combined with a metal gate electrode for use.
However, it is difficult to produce a CMOS device using two types of metals with different work functions as a gate electrode by a conventional manufacturing method. The two types of work functions are preferably equivalent to Fermi levels in widely-used poly-crystalline Si gate electrodes of the n-type and p-type MOSFET. In addition, one known method of fabricating a CMOS device using one type of metal as a gate electrode is to produce the difference between work functions by implanting boron (B), phosphorus (P), arsenic (As) ions, or the like into nickel silicide (NiSi2), followed by heat treatment. However, the difference was about 0.5 V at most and therefore a sufficient value could not be obtained from the viewpoint of circuit design.
Jpn. Pat. Appln. KOKAI Publication No. 2002-280461 has disclosed a method of introducing divalent or tetravalent metal impurities into a trivalent metal oxide to produce fixed charges and thereby causing a flat band voltage (Vfb) shift. As a result of experiments, in a system using aluminum (Al) as trivalent metal and Hf as tetravalent metal, the TDDB (time-dependent dielectric breakdown) deteriorated. The result has shown that the reliability deterioration was revealed when the introduced impurities were metals.
With the method of producing the difference between work functions in the gate electrode by implanting B, P, As ions, or the like into nickel silicide and then heat-treating the silicide, the difference in work functions between them was about 0.5 V at most and a sufficient value could not be obtained from the viewpoint of circuit design (e.g., see reference: J. Kedzierski et al., IEDM Tech., Dig. (2002) 247.